Logging in a user onto one site logs out a user on another!

I am building a CMS application. All is on one computer during development using Visual Web Developer 2008 Express Edition and Windows XP Professional.

Simply, I have one set of pages and each website's domain name points to the same pages, which load different data from the database, depending on the domain name.

I am using the membership and roles framework but have left the applicationName blank in the roleManager and membership providers so that, as authenticated users create an account, a different applicationID is created for each domain name.  This way, the users and roles are segrated into their own applications and the same usernames and role names can be used in different applications.

I have set up two domain names, one.com and two.com, with one user account on each but no roles.  I open both in separate browser windows in IE7, login the user on one.com and then log in the user on two.com.  When I return to one.com and refresh th ...